Automated microbiology: an asset to urine testing

August 2009

Automation has been a late starter in microbiology; however, it is now making up for lost time by addressing the problems associated with handling the most prolific of samples submitted for analysis. The first semi-automated laboratory urine analysers appeared on the market over 30 years ago, utilised dry chemistry dipstick technology and were mainly used in UK microbiology laboratories.

While the analysers represented an advance in automation, providing an improvement in workflow and automated the reading of the test strips, the main drawback, as time and innovation progressed, was the requirement for the operator always be present. As direct loading of patient samples was not possible, the test strips had to be dipped manually and placed on the analyser.

Analysers were used primarily as a first-line negative predictor for urinary tract infection (UTI), the technology being based on the presence or absence of biochemical markers in the urine sample – usually a combination of protein, blood/haemoglobin, nitrite or leucocyte esterase. Samples negative for these parameters indicated ‘no evidence of infection’ with a negative predictive value in the order of 96–97% and as a consequence did not require further culturing. While performing automated dipstick analysis, some laboratories continued with manual microscopy in order to visualise and report any sediment particles present.

Particle theoryThe development of particle counters based on flow cytometry with particle scattergrams or particle image capture represented the next stage in automated urine analysis. This indicated a move away from biochemical analysis to physical analysis of the urine sediment, more in tune with the reference method of urine sediment examination. Analysers could now provide not only automated microscopy but also be the starting point for introducing a UTI screening protocol and provided rack-handling systems so that patient samples could be loaded directly on the analyser. Operators were then able to leave the analyser to process the work and carry out other duties, only returning to the analyser sometime later when the work was completed.

Lean and meanMany microbiology laboratories continue to experience increasing workloads, a reduction or deskilling of staff, recruitment difficulties, mergers and consolidation of services. In addition, there are the drive for ‘Lean and mean’ working practices, targets to improve results turnaround time, and the containment or reduction of costs.

In order to cope with the current difficulties or achieve the targets and improvements sought, microbiologists continue to look towards innovation and development in automation to deliver the goods and improve their diagnostic service provision – a path that many haematology and biochemistry laboratories have followed, with the introduction of multiplexing platforms and pre- and post-analytical robotic sample handling.

Negative majorityUrinary tract infection investigation represents the largest proportion of work in microbiology, with workloads ranging from around 100 to 600 samples per day. Such workloads consume considerable time and staff resources when handled using manual methods, particularly when the majority of samples prove to be negative.

Manual microscopy remains an area where results are open to subjectivity, personal interpretation and variation in technique, particularly later in the working day when large numbers of community samples can arrive and require processing within a short space of time. Larger laboratories have introduced shifts or employ extended-hours working as a means of coping with the growth and spike in work by redeploying staff from early morning work – normally a quieter time – to cover an extended period at the end of the working day.

Different kind of analyserThe leap forward in the development and quality of digital photography technology, together with quality microscopy, has led to the introduction of a different kind of automated sediment analyser. Seemingly a contradiction in terms, the sediMAX analyser offers automated manual microscopy by producing whole-field images similar to those seen under a conventional microscope, without the associated drawbacks mentioned earlier.

The standardised and reproducible methodology uses a special disposable sample cuvette which requires just 200 microlitres of urine, aspirated from a sample volume of 2 mL. The sediMAX is a reagent-free analyser as the cuvette and distilled water – used to wash the sample probe – are the only consumables required to process the work. No reagent calibration is required and storage space for the cuvettes is minimal. The number of high power field (HPF) equivalents examined by the microscope and captured by the digital camera can be set at five, 10 15 or 20 images. Results can be reported as particles/HPF or particles/microlitre. By optimising the analytical process, the sediMAX can in effect multitask so that as one sample is analysed and reported the sample probe is washed and the next sample cuvette is being prepared for analysis. A throughput of almost 80 samples per hour is achieved with five or 10 images, so even a sudden spike in work can be handled quickly. A comprehensive range of sediment particles are covered in the recognition library against which HPF images are compared in order to produce the final report.

Evaluation mattersPerformance assessment at evaluation sites has demonstrated that sediMAX images and results compare favourably with those reported by manual microscopy techniques. By reporting results under the plus/minus system and using the classic comparison grid for semiquantitative results, sediMAX performs impressively, with 90–98% of results for red blood cells (RBC), white blood cells (WBC) and epithelial cells agreeing within a factor of one.

Possible carryover from positive to negative samples is an area of concern in the laboratory to ensure that false-positive results are not being generated as a result of inadequate probe washing. However, analysis of samples with high WBC, RBC and bacterial counts prior to testing a negative sample has demonstrated just how effective the wash facility is on the sediMAX analyser. The small sample volume (2 mL) and aspirated analytical volume (200 microlitre), which is completely dispensed into the cuvette, results in only trace amounts of urine coating the external and internal surfaces of the sample probe. Set against this residual coating of urine, the 6-mL distilled water wash volume ensures no carryover between samples.

Filters in the Menasoft data manager software allow the laboratory to set-up screening protocols, with UTI screening usually at the top of the list. Using a combination of WBC, RBC, bacteria and/or epithelial cells, laboratories can screen out negative samples confidently and report them the same day, while at the same time realising a reduction in the number of samples requiring culturing and the costs involved. Initial performance studies comparing sediMAX UTI screening with conventional culture methods have shown that sediMAX is capable of reducing the culture workload by up to 46%, with a negative predictive value of 96% (data on file).

Walkaway systemWith 100-sample capacity and 600 sample cuvettes onboard, sediMAX delivers a true load, start and walkaway system for urine sediment analysis which ensures quality of results by any operator and allows staff to concentrate on other tasks.

In a bid to work as effectively as possible, many microbiology laboratories are considering the introduction of the ‘slimline’ primary collection tube to replace the standard 30 mL universal container. Such sample tubes can be checked in quickly, barcoded and placed directly in the tube racks, thus negating the need for subaliquoting of larger-volume primary bottles.

While the slimline tube generally costs a little more than a universal container, this can be offset against the reduction in number of samples requiring culture and the costs of a secondary sample tube. There is also the additional benefit of reducing manual sample handling and the general improvement in health and safety issues.

Scottish perspectiveThe microbiology department at the Southern General Hospital, Glasgow, took delivery of two sediMAX analysers in January 2009 as a replacement for an aged UF100 and to handle the workload from the combined Southern General and Victoria hospitals.

Gordon Mackie, senior biomedical scientist, explains: “The bulk of the 280 samples per day arrive mid-afternoon between 3.30 and 5.00 pm; however, the throughput of the analysers means we have no problem in processing all the work before the end of day. By applying a UTI screening protocol, negative samples are reported the same day. This accounts for approximately 60% of the samples analysed. Not only has this improved the results turnaround time but also has reduced the time involved with urine culture and the associated costs.

“We realised straight away that sediMAX was a different way of carrying out automated urine analysis and was more in tune with traditional manual methods. Unlike our previous flow cytometry system, the quality of the images obtained with sediMAX enables staff to view whole-field images, if required, on screen. This is particularly useful with crowded samples or when we may want to double-check results, so time spent on manual reviews has now fallen to almost zero.”

Gordon adds: “The small HPF image preview screen in the results database has also proved popular with staff, as abnormalities can be recognised easily and then followed up quickly by simply clicking the preview image and viewing the more detailed full-screen images.”

Biomedical scientist Charlie McKenna adds: “The sediMAX requires very little maintenance, with a daily shutdown and clean taking around 10 minutes, and there is no requirement for extra weekly or monthly maintenance. The morning start-up takes only five minutes to top-up the distilled water and replenish the sample cuvettes. Once quality control has been run to verify and confirm system performance, patient samples can be loaded.

“Medical laboratory assistants have found the system much easier and simpler to operate than our previous analyser. From powering up the PC and analyser, the system is ready to run in five minutes, making it ideal for on-call use. The simplicity of the system and easy-to-use operating software also means training requirements are minimal.

In conclusion, Gordon says: “sediMAX is proving an excellent asset to the department. It can be a worry when changing to a different supplier but the Menarini service and support team has been first class in helping us make the transition from one technology to another.”